This map displays predicted probability of a 12-digit Hydrologic Unit (HUC12) being at risk of violating the drinking water nitrate standard. Risk is defined as there being greater than a 50% chance of having a drinking water violation. Observed violations of the nitrate standard in public drinking water was used to make predictions across the conterminous United States. The data on nitrate violations comes from the EPA's Safe Drinking Water Information System (SDWIS) and the data used as predictor variables in the prediction models comes from EPA's StreamCat database. The original predictions were made at the National Hydrography Dataset (NHD) Catchment scale and summarized at the HUC12 scale and/or 300 m pixel scale. The maps show that 19% of the conterminous United States is at risk of groundwater sourced drinking violations, while 16% of the U.S. is at risk of nitrate violations from surface water sources. Regions with the highest risk of nitrate drinking violations from groundwater sources are found in the southwest, south central plains, parts of north west, mid-Atlantic. Surface water sourced nitrate violations have the greatest risk primarily in the southwest and south-central areas of the U.S. This dataset was produced by the US EPA to support research and online mapping activities related to EnviroAtlas. EnviroAtlas (https://www.epa.gov/enviroatlas) allows the user to interact with a web-based, easy-to-use, mapping application to view and analyze multiple ecosystem services for the contiguous United States. The dataset is available as downloadable data (https://edg.epa.gov/data/Public/ORD/EnviroAtlas) or as an EnviroAtlas map service. Additional descriptive information about each attribute in this dataset can be found in its associated EnviroAtlas Fact Sheet (https://www.epa.gov/enviroatlas/enviroatlas-fact-sheets).